1. Field of the Invention
The present invention relates generally to a frequency overlay system. More particularly, the present invention relates to a system and method for transmitting and receiving frequency allocation information based on identification information in a frequency overlay system.
2. Description of the Related Art
In general, frequency resources of 5˜20 MHz are allocated to Mobile Stations (MSs) according to the Institute of Electrical and Electronics Engineers (IEEE) 802.16m standard. Available frequency resources of a Base Station (BS) are divided into a plurality of Frequency Allocations (FAs) which can be allocated to each MS serviced by the BS. In the IEEE 802.16m standard, a one-dimensional resource allocation scheme is used due to its low complexity, small overhead, separate coding MAP message, and high link adaptation gain of a MAP Information Element (IE) of each MS.
Frequency overlay is used to support MSs using various bandwidths. Thus, frequency resources of the BS are divided into multiple FAs and an MS accesses each FA according to an available bandwidth. Accordingly, a one-dimensional resource allocation algorithm of separate coding capable of efficiently operating using the multi-FA is provided to a frequency overlay system.
FIG. 1 illustrates a frequency overlay system having two 10-MHz FAs according to the related art.
Referring to FIG. 1, when frequency resources of 20 MHz are allocated, a BS 140 of the frequency overlay system divides the frequency resources allocated to the BS 140 into two 10-MHz FAs. Here in, the first FA (FA#1) is allocated to an MS-A 110 and the second FA is allocated to an MS-C 130, while, FA#1 and FA#2 are allocated to an MS-B 120. In this way, both the MSs capable of accessing 10 and 20 MHz bandwidth can be supported under the same BS's frequency resources of 20 MHz.
The concept of a separate coding MAP message will be described using FIG. 1. The IEs of the MAP message are encoded for each MS. The BS controls a Modulation and Coding Selection (MCS) level by the MAP message. When separate coding is used, power for each IE is allocated according to the current channel state of a designated MS instead of an MS who experiences the worst communication state. In the separate coding MAP message, each IE is considered as one MAP message and a Cyclic Redundancy Check (CRC) field is added to the end of each IE. This additional overhead problem is mitigated by removing a Connection IDentifier (CID) field of an MS from each IE. In this case, each IE is individually scrambled in a method in which the IE can be detected and decoded by only a specific MS. When the separate coding MAP message is used, a method in which each MS is not required to detect MAP lEs of other MSs shall be used.
FIGS. 2A to 2C illustrate protocol structures in a frequency overlay system according to the related art.
Referring to FIGS. 2A to 2C, various protocol structures for frequency overlay capacity of the system are provided. The most simplified protocol structure is a single-FA protocol structure illustrated in FIG. 2A. In the single-FA protocol structure, Media Access Control (MAC) layers 202, . . . , 204 and physical layers 206, . . . , 208 are separated and each frequency is allocated through the separated layers. However, the separations in MAC and physical layers limit the amount of information that can be shared among FAs. This deficiency of the shared information inevitably increases an unnecessary overhead from MAC processing processes of MAC layers such as those in network entries, bandwidth requests, or Quality of Service (QoS) which have to be repeated in each FA.
To mitigate the above-described problem, a frequency overlay protocol structure as illustrated in FIG. 2B includes one common MAC layer 210 and a plurality of physical layers 212, . . . , 214. Each physical layer is associated with each FA. The structure as illustrated in FIG. 2B is referred to as a multi-FA protocol structure. Since the common MAC layer can be efficiently harmonized with each FA in the multi-FA protocol structure, a MAC overhead may be reduced by avoiding repeatedly processing a plurality of FAs. However, a MAC packet needs to be encoded in multiple physical packets since there is a plurality of physical layers, and a physical packet encoded within each physical layer leads to additional overhead since one additional CRC field is required for each physical packet. Here, a MAP IE is independently created and transmitted for each FA.
To mitigate an overhead problem occurring in frequency resource allocation, a frequency overlay protocol structure having one MAC layer 216 and one physical layer 218 may be used as illustrated in FIG. 2C. Since there is only the single physical layer in the structure, a MAC packet is encoded in one physical packet and the one physical packet is classified into FAs that are available later 200, . . . , 222. A single MAP IE may be used to indicate frequency resource allocation within multiple FAs, thereby reducing an overhead occurring in frequency resource allocation in the frequency overlay system.
A frequency resource allocation scheme applied to the IEEE 802.16m standard is a one-dimensional allocation scheme.
FIGS. 3A to 3D illustrate one-dimensional allocation schemes according to the related art.
Referring to FIGS. 3A to 3D, the one-dimensional allocation schemes include a start-length allocation scheme (illustrated in FIG. 3A), a run-length allocation scheme (illustrated in FIG. 3B), a tree-based allocation scheme (illustrated in FIG. 3C), and a pattern-based allocation scheme (illustrated in FIG. 3D).
In the start-length allocation scheme illustrated in FIG. 3A, frequency resource allocation of each MS is classified by a starting point and a length of allocated frequency resources. In the tree-based allocation scheme illustrated in FIG. 3B, tree-structured nodes are used to indicate all frequency resources of a BS and frequency resources allocated to each MS are indicated by a node ID of a corresponding node. In the run-length allocation scheme illustrated in FIG. 3C, frequency resource allocation for each MS is classified by only a length of allocated frequency resources. In this case, each MS detects all length fields allocated to previous MSs in order to compute a starting point.
The pattern-based allocation scheme illustrated in FIG. 3D uses continuous bits to indicate a frequency resource allocation pattern allocated to each MS.
The four allocation schemes are well known. Among the four allocation schemes, the run-length allocation scheme has a smallest MAP overhead in a joint coding MAP message and each MS may detect all individual MAP lEs of other MSs. On the other hand, the tree-based allocation scheme has a smallest overhead in the case of a separate coding MAP message and each individual MAP IE may be detected by only a corresponding MS.
However, there is a problem in that a conventional MAP IE format for frequency resource allocation between FAs leads to a significant overhead.
Therefore, a need exists for a system and method for reducing MAP overhead in frequency resource allocation between FAs.